It started yesterday. Extremely loud noise... sounding something like mixer or like drill. I mean not identical, heh, just this sound makes me think of these. Like something's spinning. Yesterday sound was constant. Today morning I opened the case and removed as much dust as I could handle although I'm not 100% sure I got rid of enough of it. So when I turned it on today at first sound was gone (yay) but then it appeared again, as loud as yesterday. After a longer while it became quieter and eventually disappeared again. I had some moments (long enough to wonder that maybe I fixed it) of silence and then it started again. Now it comes and goes.

What I could do about it? Am I even on right track? Maybe cleaning it helped but maybe I missed some dust and I need to try again? Or just some fan is dying and I need to replace it? But cleaning helped so maybe it's really just dust?

Don't ask me which part of computer it is because I don't have a clue... it's so loud that I can't really tell. It feels like this sound is everywhere, it took me a while to even realize that it's computer.

If you said that the sound disappeared at first and reappeared and then after some time disappeared, check wires inside the case. I've seen cases with exactly same behavior where a wire would fall into the fans and cause nose. Once the computer is moved a little bit, it would fall off the fans an stop making noise.
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AndrejaKoOct 1 '10 at 12:20

4 Answers
4

It's a fan. To find out which one, stop the fans one at a time using a pencil or finger and see if it goes away. You can buy a new one, or you can do the Sanford and Son fix:

Here's how:

There's usually a circle shaped label in the center of the fan on the blow side. Peel off the label. Under it, you will find a rubber plug. Pull this out. Under that, you will find a small plastic lock ring which holds the fan shaft in place. Use a tiny flat blade screwdriver to pop this lock ring off. Pull out the fan/shaft assembly. There will probably be some dark grimy junk on the surfaces revealed. Use compressed air to clean it. Maybe some alcohol with a cotton swab for the stubborn spots. Then, get a tiny dab of general purpose grease and put it on the metal shaft. Reinstall.

Probably one of the fans has a dodgy bearing. When it's making the noise put your finger on each of the fans to stop it and see if that stops the noise. Then, you can replace the fan. Be careful when poking around the power supply as that has mains voltages in it.

Once I had a CD explode in my drive, that made a really loud grinding noise every time it tried to spin the CD and read it.
Opening the drive, it spat out the tray, and I found probably 20 pieces that formed most of the disk, the rest of the pieces were too small, and had got stuck in different parts of the drive. I just removed that drive and replaced it.